Conventional belt retractors comprise a frame, a belt reel rotatably mounted in the frame, and an energy converter coil having at least one metal strip.
Such belt retractor is known from the German Patent Application 19 13 448. The energy converter coil consists of a metal strip which is accommodated in a drum in a first direction along the inner wall thereof. One end of the metal strip is connected with the drum with which the belt reel is connected as well. The other end is connected with a shaft which has a blocking wheel. In the blocking wheel a blocking pawl can engage, which is actuated by a vehicle-sensitive sensor. In the initial condition, the blocking wheel can rotate freely, so that the unit comprising shaft, metal strip, drum and belt reel can rotate freely. As soon as the blocking pawl engages in the blocking wheel, the shaft is locked in place. If in this condition particularly high forces act in the safety belt, such a high torque will be active between the drum and the shaft that the metal strip accommodated in the drum is wound up onto the shaft in a direction which is opposite to the direction in which the metal strip was accommodated in the drum originally. In this process, the metal strip is bent twice, namely first by about 180°, so that the metal strip extends in the opposite direction, and is then bent back a bit, so that the metal strip conforms to the curvature of the shaft. This bending resistance acts as resistance torque between the drum and the shaft, which in a known manner represents a limitation of the force maximally acting in the safety belt.
The disadvantage of this known construction consists in that there is an asymmetrical force distribution in the energy converter coil.
Thus, the object of the invention consists in developing a belt retractor as mentioned above such that more uniform force conditions are obtained.